The Economist at the Nuclear Summit in London on 15 April. (Courtesy: Margaret Harris)"> Predicting nuclear's next big thing: Charles Oppenheimer of Oppenheimer Energy, Najat Mokhtar of the International Atomic Energy Agency and Vijay Vaitheeswaran of The Economist at the Nuclear Summit in London on 15 April. (Courtesy: Margaret Harris) In scientific terms, fission and fusion are two sides of the same coin. The first produces energy by splitting big atomic nuclei into two or more pieces. The second produces it by combining two or more small nuclei into a larger one. In both cases, the difference between the mass you start out with and the mass you end up with determines how much energy you get, following Einstein’s famous equation E = mc 2 . Practically speaking, though, fission and fusion are worlds apart. Fission power plants have been putting electrons on the grid since the 1950s.…